This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-324677 filed on Oct. 19, 2000.
1. Field of the Invention
The present invention relates to an air amount detector for an internal combustion engine, which detects a flow amount of intake air and calculates an air amount inside cylinder.
2. Description of Related Art
In general, methods for measuring an air amount inside cylinder of an engine are classified broadly in two schemes: One is a method in which an intake air flow is detected by an airflow meter, and then the air amount inside cylinder is calculated based on the detected value (hereinafter referred to as a mass-flow system); and the other is a method in which an intake air pressure is detected by an intake air pressure sensor, and then the air amount inside cylinder is calculated based on the intake air pressure and rotation speed of the engine (hereinafter referred to as a speed-density system). The mass flow system has an advantage of having a measurement accuracy of the air amount inside cylinder under a steady state because the intake air flow equals the air amount inside cylinder under the steady state. However, during a transient period, a response of the airflow meter delays (e.g., in a case of a thermo airflow meter, a response is delayed due to the heat mass of a sensor portion of the airflow meter itself). Thus, the massflow system has a disadvantage of an undesirable response during the transient period.
On the contrary, the speed-density system has better response during the transient period than the massflow system has. This is due to a high response of an intake air pressure sensor.
In view of the above, a system that combines two sensors having advantages of the massflow system and the speed-density system has been developed recently. The two-sensor combination system uses an airflow meter and an intake air pressure sensor provided therein so that the air amount inside cylinder is calculated based on the intake air flow detected by the airflow meter during the steady period while it is calculated based on the engine speed and the intake air pressure detected by the intake air pressure sensor.
In the above-described two-sensor combination system, the air amount inside cylinder is calculated based on the engine speed and the intake air pressure detected by the intake air pressure sensor. However, the air amount inside cylinder changes by depending not only on the intake air pressure, but also on volumetric efficiency and an intake air temperature, so that a calculation result of the air amount inside cylinder may have a margin of error due to an influence of a detection error or the like. There is an increasing demand for an engine developed in recent years to have a fuel-air ratio controller of high precision in order to deal with an exhaust gas cleaning regulation. In order to achieve such demand, it is necessary to improve the calculation accuracy of the air amount inside cylinder.
An object of the present invention is to provide an air amount inside cylinder detector for an internal combustion engine that enables to improve the calculation accuracy of the air amount inside cylinder.
According to the present invention, a response delay of an intake air flow detection means for detecting a air flow of the intake air flowing in an intake air passageway of the internal combustion engine is compensated by response delay compensation means. An intake air system model is used for modeling a behavior of an intake air which passes through a throttle valve and flows into cylinders, so that an output of the response delay compensation means is input to the intake air system model to calculate an output of the intake air system model as an air amount inside cylinder by a calculation means. In this case, because the response delay compensation means for compensating the response delay of the intake air flow detection means is provided, it is possible to calculate the air amount inside cylinder from a detection value of the intake air flow amount even during the transient period with a desirable response, thereby enabling to improve calculation accuracy of the air amount inside cylinder.